The present invention is directed to reinforced oxymethylene polymer molding compositions.
Oxymethylene polymer molding compositions have been employed for many years. In order to enhance various physical properties of such compositions, various fillers have been employed. However, oxymethylene polymer compositions, in contrast to other types of molding compositions based on nylon or polybutylene terephthalate, have been found to generally be incompatible with added filler materials in that the fillers tend to migrate to the surface of the composition during the molding process. Such stratification of the filler is very undesirable since the physical properties of the resulting molded article are not uniform. It is therefore desirable to provide an oxymethylene molding composition which comprises an added filler material but which can be melt processed while avoiding the above-noted problems.
It is also known to employ a reinforcing fiber in an oxymethylene molding composition. See, for example, commonly-assigned U.S. Pat. No. 3,455,867, herein incorporated by reference. However, the presence of a reinforcing fiber in a molding composition, while generally enabling desirable results to be achieved, can result in a shaped article produced therefrom becoming warped due to the fact that such reinforcing agents are highly elongated in form. However, the substitution of a particulate filler for a reinforcing fiber, while desirable for the reasons noted above, can also result in the formation of a shaped article of decreased mechanical properties since the fibrous reinforcing agent inherently provides greater reinforcement than does a particulate filler. It is thus also desirable to provide an oxymethylene molding composition which comprises an added filler and which enables a shaped article to be produced therefrom of desirable mechanical properties and enables lessened amounts of fibrous reinforcing agents to be employed.